A great deal of attention has been given to the issues relating to missile guidance for destroying stationary or moving targets. During World War II, antiaircraft cannon were operated in a manner that attempted to estimate the future location of an aircraft at the time that a shell would arrive at its altitude and range, and fired at the estimated location. Such antiaircraft artillery would seldom result in the actual striking of an aircraft with the shell, but relied on the fragments from the explosion of the shell to damage or destroy the aircraft.
World War II also saw the introduction of analog-computer control systems for estimating the location of targets, both fixed and moving, and for controlling the aiming of various cannon to fire at a predicted future location of the target. Artillery shells, whether land-based, naval, or airborne, used explosives to increase the likelihood of damage to the target even in the case of a near miss.
With the emergence of ballistic threat missiles, intercept reliance could not be placed on the destructive power of an explosive warhead. The kill vehicle was required instead to actually impact on the target vehicle, thus becoming a kinetic kill vehicle. The guidance systems used for early kinetic-kill vehicles employed extensions of the older techniques. More particularly, the location, speed and acceleration (states) of the target vehicle are sensed, and the future path estimated. The kinetic-kill vehicle is accelerated toward an impact point that is predicted based upon the location, speed and acceleration of the kill vehicle, with the expectation that the kill and target vehicles will collide at the predicted intercept point. One may readily understand that many problems arise in the control and guidance of the kill vehicle under such conditions, not the least of which is the problem of sensing the actual location, speed and acceleration, if any, of the target vehicle, and determining its future path. The acceleration, in turn, of the target vehicle depends upon its rocket or propulsion thrust, its mass, gravity and aerodynamic loading (if not exoatmospheric). Similar considerations apply to the kill vehicle, although its parameters are likely to be under the control of the operator or designers of the kill vehicle.
There have been in the last few years high-profile failures of kill vehicles to intercept their test targets. It has been determined that at least one of the reasons for the failures is that the guidance algorithms assume that the total rocket motor impulse of the kill vehicle and other vehicle parameters are known, thereby providing a mathematical basis to compute a predicted intercept point. However, the rocket motor impulse is not constant, so the thrust, and the mass properties of the kill vehicle, may deviate from the assumed values, with the result that the kill vehicle approaches the predicted intercept point with a speed along its thrust vector that is different than its predicted speed. This difference between the predicted and actual speed may, in turn, result in the kill vehicle arriving at the predicted intercept point either before or after the target vehicle's arrival. This, in turn, results in a miss.
Improved guided missile targeting systems are desired.